Polyoxymethylenes (POM), also known as polyacetals, are well established as exceptionally useful engineering materials in a variety of applications. Polyoxymethylenes generally exhibit excellent mechanical properties, fatigue resistance, abrasion resistance, chemical resistance, lubricity, and moldability. Compositions comprising polyoxymethylene are particularly useful in preparing articles by extrusion, compression molding, injection molding, blow molding, rotational molding, melt spinning, stamping, and thermoforming techniques commonly used with thermoplastic materials. Finished articles made from such compositions possess the aforementioned desirable properties associated with polyoxymethylenes, and accordingly find utility in constructing molded parts across a broad range of technologies, for example, in automotive, industrial/machinery, consumer goods and electrical/electronic applications.
In many applications, it is often important that the polyoxymethylene compositions have good mechanical properties including toughness and stiffness, especially when exposed to heat. Unreinforced polyoxymethylene compositions often have good elongations at yield and wear resistance, but can have insufficient stiffness, particularly at elevated temperatures. Additives such as mineral fillers and fibrous reinforcing agents are often used to improve the physical properties of polymeric compositions. When reinforcing agents are incorporated in polyoxymethylene compositions, increased impact strength can come at the expense of other material properties including, for example, wear resistance and ductility. It would therefore be desirable to provide polyoxymethylene compositions having balanced physical properties. Of particular interest are polyoxymethylene compositions having high impact strength without causing a significant reduction in other properties, which has heretofore not been possible with conventional polyoxymethylene compositions.
Optimizing modulus-impact balance refers to a composition having a property profile where the impact strength is increased significantly with minimal or no effect on modulus. Furthermore, other enabling properties of polyoxymethylene compositions, including thermal properties, are not expected to be affected in a modulus-impact balanced composition. Polyoxymethylene composite materials having these desired properties have been the subject of intensive research and development. Optimizing mechanical and thermal properties has largely been focused on tuning interfacial interactions between polymer matrix and filler components by, for example, sizing the fillers, functionalizing the polymer matrices, and compatibilizing the composites through additives or copolymers.
Nonetheless, there remains a continuing need for reinforced polyoxymethylene compositions having high impact strength in addition to good overall mechanical properties and thermal stability.